>>>> Also when I want to move a child frame to the left of its parent via
 >>>>
 >>>>     (modify-frame-parameters nil '((left . 0)))
 >>>>
 >>>> the left border disappears.  Is that intended?
 >>>
 >>> If I understand that correctly, then probably yes. The borders are drawn
 >>> around the frame, so the left border is at left - 1, the right at left +
 >>> width + 1, and so on.
 >>
 >> I see.
 >>
 >>> Whatever is outside of the terminal is clipped.

Troublesome.  Please revise that.  When I want to resize a child frame
with the mouse, I have to drag its internal border.  But as it stands,
the internal border is part of the underlying or root frame and the
whole make_lispy_position mechanism is broken on ttys.

 > _Much_ nicer than the default IMO. I still wished Emacs would do that by
 > default, but here were objections.

Looks good.  But _where_ on earth (that is, in the code) do you that and
how is it related to the width of the internal border?

I attach my latest achievements both in the menu bar and mouse drag
child frame departments.  Menu bars now accept navigation with the
keyboard which was pretty non-trivial to do.  Mouse dragging works with
header and mode lines - the attached tty-child-frames.el should provide
the necessary ingredients via C-l and M-l.

One bug I noted now is the following.  Do C-l and M-l and drag the
yellow and orange frames somehow as in before.png with the cursor in the
yellow frame right before the left edge of the orange frame.  Do C-f -
the cursor appears on top of the left edge of the orange frame as in
middle.png.  Another C-f moves it into the orange frame as in after.png.

martin